在软土中修建浅埋大跨小净距隧道下穿高速公路连续梁桥,会造成土体侧移,危及桥梁桩基的稳定,存在很高的风险。在分析工程难点的基础上,采用数值方法分析隧道开挖造成连续梁桥应力变形规律,提出复合锚杆桩加固技术。通过系统的数值建模计算和现场监测实验,研究了锚杆桩注浆范围和桩长对桥梁结构稳定性的影响。结果表明:(1)复合锚杆桩通过钻孔中加筋和高压注浆模式,在核心形成小直径(15 cm)钢筋混凝土桩的同时,高压注浆加固桩周土体,共同形成大直径水泥土桩(可达200 cm),通过排桩布局包围被保护桥桩,保护效果较好;(2)复合锚杆桩利用自身的刚度隔绝了大跨度软土隧道开挖导致的应力释放,从而抵制了围岩变形传递,具有良好的应力应变隔离作用,通过高压注浆形成的水泥土复合桩也加固了隧道围岩,从而缩小隧道塑性破坏区;(3)复合锚杆桩的注浆范围和长度对于克服桥墩变形具有显著影响,注浆范围达到2 m时,隧道开挖完成之后桥梁桩基水平位移减少95%,当复合锚杆桩伸长至隧道以下时,位移减小了85%,此时隔离保护作用才能发挥最大效果。

The construction of a shallow-buried large-span and small-clear distance tunnel under a freeway continuous beam bridge in soft soil can cause soil lateral movement, threaten the stability of the bridge pile foundation, and lead to cracking of the continuous beam bridge structure, posing a high risk. In this paper, based on the analysis of the difficulty of a tunnel project, the stress deformation law of continuous beam bridge caused by tunnel excavation is analyzed using numerical methods, and the composite anchor-pile reinforcement technology is proposed. The influence of grouting range and pile length on the stability of bridge structure is studied by numerical modeling and field monitoring experiment. The results show that: (1) The composite anchor pile is reinforced in the core through reinforcement and high-pressure grouting mode, and at the same time as the core forms a small-diameter (15 cm) reinforced concrete pile, the high-pressure grouting strengthens the soil around the pile, and jointly forms a large-diameter cement-soil pile (up to 200 cm). The protected bridge piles are surrounded by a row of piles to achieve excellent protection effect; (2) The composite anchor pile utilizes its own stiffness to isolate the stress release caused by the excavation of the long-span soft soil tunnel, thereby resisting the deformation transmission of the surrounding rock and exhibiting a good stress-strain isolation effect. At the same time, the cement-soil composite pile formed by high-pressure grouting also strengthens the surrounding rock ofthe tunnel, thereby narrowing the plastic failure area of the tunnel and protecting the bridge pile. (3) The grouting range and length of the composite anchor pile have a significant impact on overcoming the deformation of the bridge pier, and when the grouting range reaches 2m, the horizontal displacement of the bridge pile foundation is reduced by 95% after the tunnel excavation is completed. When the composite anchor pile is elongated below the tunnel, the displacement is reduced by 85%, so that the isolation protection can be maximized.